Novel avermectins are produced from known microorganisms

ABSTRACT

Incubation of 13-deoxy ivermectin aglycone with a species of B. subtilis and of S. griseus results in the production of 13-β ivermectin monoglucopyranoside as the major product and of 5-β ivermectin monoglucopyranoside as the minor product.

BACKGROUND OF THE INVENTION

The avermectin family, of which invermectin is a member, encompasses a series of very potent antiparasitic agents that are useful against a broad spectrum of endoparasites and ectoparasites in mammals as well as being useful in agriculture against various parasites found in and on crops and in soil. Ivermectin is disclosed in U.S. Pat. No. 4,199,569 issued Apr. 22, 1980 to Chabala and Fisher.

The avermectins possess a disaccharide moiety at the 13-position consisting of the α-L-oleandrosyl-α-L-oleandrosyl group. This disaccharide moiety may be removed as described in U.S. Pat. No. 4,206,205 to produce the corresponding aglycone derivatives having an hydroxy group at the 13-position. The 13-hydroxy group may be removed as described in U.S. Pat. Nos. 4,171,314 and 4,173,571 to form the corresponding 13-deoxy compounds.

Another family of compounds, identified as the milbemycin family, that are disclosed in U.S. Pat. No. 3,950,360 has the same 16 membered ring as the avermectin compounds, although they lack the disaccharide moiety and also differ in some substituent groups.

A major goal of research is to provide new, active avermectin and milbemycin compounds.

OBJECTS OF THE INVENTION

It is, accordingly, an object of the present invention to provide new ivermectin compounds. Another object is to provide processes for the preparation of these new ivermectin compounds. A further object is to provide methods and compositions for using these new ivermectin compounds. These and other objects of the present invention will be apparent from the following description.

SUMMARY OF THE INVENTION

Incubation of 13-deoxy ivermectin aglycone with a mixed culture system of induced resting cells of Bacillus subtilis and of Streptomyces griseus results in two biotransformation products, 13-β ivermectin monoglucopyranoside as the major product and 5-β ivermectin monoglucopyranoside as the minor product.

DETAILED DESCRIPTION

In accordance with this invention, two novel compounds are described, which are prepared by growing, under controlled conditions with 13-deoxy ivermectin aglycone as a substrate, a mixed culture of two microorganisms, Bacillus subtilis strain MB-4974 and Streptomyces griseus strain HCA-185. The compounds are obtained by fermentation and recovered in substantially pure form as described herein.

The culture of B. subtilis designated MB-4974 is in the culture collection of Merck & Co., Inc., Rahway, N.J. A sample of this culture, capable of producing the herein described compounds in conjunction with the culture of S. griseus designated HCA-185, is available in the permanent culture collection of the American Type Culture Collection at 12301 Parklawn Drive, Rockville, Md. 20852, and has been assigned the accession number ATCC 55060.

The culture of S. griseus designated HCA-185 is also in the culture collection of Merck & Co., Inc., Rahway, N.J. A sample of this culture, capable of producing the herein described compounds in conjunction with the culture of B. subtilis designated MB-4974, is available in the permanent culture collection of the American Type Culture Collection, supra, and has been assigned accession number ATCC 55070.

The above-mentioned microorganisms are illustrative of the strains of B. subtilis and of S. griseus which can be employed in the joint production of 13-β ivermectin monoglucopyranoside and of 5-β ivermectin monoglucopyranoside. It is to be understood, however, that mutants of the above-mentioned organisms, for example, those 5-β and 13-β ivermectin monoglucopyranoside-producing mutants that are obtained by natural selection or those produced by mutating agents including x-ray irradiation, ultraviolet irradiation, nitrogen mustard or like treatments also are included within the scope of this invention.

The instant compounds are produced from 13-deoxy ivermectin aglycone during the aerobic fermentation of suitable aqueous nutrient media under conditions described hereinafter, with a mixed culture system of Bacillus subtilis MB-4974 and Streptomyces griseus HCA-185. Aqueous media such as those used for the production of many antibiotic substances are suitable for use in this process for the production of these macrocyclic compounds. Such nutrient media contain sources of carbon and nitrogen assimilable by the microorganism and generally low levels of inorganic salts. In addition, the fermentation media may contain traces of metals necessary for the growth of the microorganisms, and production of the desired compounds. These are usually present in sufficient concentrations in the complex sources of carbon and nitrogen, which may be used as nutrient sources, but can, of course, be added separately to the medium if desired.

The 5-β ivermectin monoglucopyranoside and 13-β ivermectin monoglucopyranoside compounds of the present invention can be used separately or jointly.

The starting material for the present invention is 13-deoxy ivermectin aglycone which can be produced as disclosed in U.S. Pat. Nos. 4,171,314 and 4,173,571, and in an article by Mrozik et al., Tetrahedron Letters 24 (48): 5333-5336 (1983).

The following media were used in the following examples.

    ______________________________________                                                           g/l                                                          ______________________________________                                         1.       Soy Glucose Medium                                                             Dextrose       20.0                                                            Soya meal      5.0                                                             Fidco yeast extract                                                                           5.0                                                             NaCl           5.0                                                             MES buffer     9.8                                                             Adjust pH to 7.0                                                      2.       Medium A                                                                       Dextrose       1.0                                                             Dextrin        10.0                                                            Beef extract   3.0                                                             Ardamine pH    5.0                                                             NZ Amine Type E                                                                               5.0                                                             MgSO.sub.4.7 H.sub.2 O                                                                        0.05                                                            K.sub.2 HPO.sub.4                                                                             0.3                                                             Adjust pH to 7.1                                                               Add CaCO.sub.3 0.5                                                    3.       Medium B                                                                       Glucose        10.0                                                            Hycase SF      2.0                                                             Beef extract   1.0                                                             Corn Steep Liquor                                                                             3.0                                                             Adjust pH to 7.0                                                      ______________________________________                                    

Other aqueous media such as those used for the production of many antibiotic substances are suitable for use in the process for the production of this macrocyclic compound.

Such nutrient media contain sources of carbon and nitrogen assimilable by the microorganism and generally low levels of inorganic salts. In addition, the fermentation media may contain traces of metals necessary for the growth of the microorganisms, and production of the desired compound. These are usually present in sufficient concentrations in the complex sources of carbon and nitrogen, which may be used as nutrient sources, but can, of course, be added separately to the medium if desired.

In general, carbohydrates such as sugars, for example glucose, sucrose, maltose, lactose, dextran, cerelose, corn meal, oat flour, and the like, and starches are suitable sources of assimilable carbon in the nutrient media. The exact quantity of the carbon source which is utilized in the medium will depend, in part, upon the other ingredients in the medium, but it is usually found that an amount of carbohydrate between 1 and 10 g/l in the medium is satisfactory. These carbon sources can be used individually or several such carbon sources may be combined in the same medium.

Various nitrogen sources such as yeast hydrolysates, yeast autolysates, yeast cells, tomato paste, corn meal, oat flour, soybean meal, casein hydrolysates, yeast extracts, corn steep liquors, distillers solubles, cottonseed meal, meat extract and the like, are readily assimilable by S. erythraea, in the production of the instant compounds. The various sources of nitrogen can be used alone or in combination in amounts ranging from 1 to 5 g/l in the medium.

Among the nutrient inorganic salts which can be incorporated in the culture media are the customary salts capable of yielding sodium, potassium, magnesium, ammonium, calcium, phosphate, sulfate, chloride, carbonate, and like ions. Also included are trace metals such as iron, zinc, manganese, copper, boron, molybdenum and the like.

It should be noted that the media described hereinbelow and in the Examples are merely illustrative of the wide variety of media, which may be employed, and are not intended to be limiting.

The following are examples of media suitable for growing strains of B. subtilis and of S. griseus.

    ______________________________________                                         COMPOSITION OF MEDIA                                                           ______________________________________                                         MEDIUM 1                                                                       Glucose                50     g                                                NaCl                   5      g                                                (NH.sub.4).sub.2 SO.sub.4                                                                             2      g                                                CaCO.sub.3             6      g                                                Soya Flour Extract     30     g                                                Distilled Water        1000   ml                                               Adjust pH to 7.0                                                               MEDIUM 2                                                                       Dextrose               20     g                                                Peptone                5      g                                                Meat Extract           5      g                                                Primary Yeast          3      g                                                NaCl                   5      g                                                CaCO.sub.3             3      g                                                Distilled Water        1000   ml                                               Adjust pH to 7.0                                                               MEDIUM 3                                                                       Soluble Starch         10     g                                                Ardamine pH            5      g                                                NZ amine E             5      g                                                Beef Extract           3      g                                                MgSO.sub.4.7H.sub.2 O  0.5    g                                                Cerelose               1.0    g                                                Na.sub.2 HPO.sub.4     0.190  g                                                KH.sub.2 PO.sub.4      0.182  g                                                CaCO.sub.3             0.05   g                                                Distilled Water        1000   ml                                               MEDIUM 4                                                                       Cerelose               10     g                                                Corn Starch            40     g                                                Glycine                7.5    g                                                Tyrosine               0.9    g                                                Triolein               2.5    g                                                NaCl                   2.0    g                                                K.sub.2 HPO.sub.4      1.56   g                                                KH.sub.2 PO.sub.4      0.78   g                                                MgSO.sub.4.7H.sub. 2 O 0.5    g                                                CoCl.sub.2.6H.sub.2 O  0.001  g                                                FeSO.sub.4.7H.sub.2 O  0.02   g                                                MnCl.sub.2.4H.sub.2 O  0.001  g                                                ZnSO.sub.4.7H.sub.2 O  0.05   g                                                CaCO.sub.3             3.0    g                                                Distilled Water        1000   ml                                               MEDIUM 5 (SLANT)                                                               Yeast Extract          4      g                                                Malt Extract           10     g                                                Dextrose               4      g                                                Bacto Agar             20     g                                                Distilled Water        1000   ml                                               Adjust pH to 7.0                                                               MEDIUM 6                                                                       Cerelose               15     g                                                Soybean meal           15     g                                                CaCO.sub.3             1.0    g                                                Distilled Water        1000   ml                                               Adjust pH to 7.0-7.2                                                           ______________________________________                                    

The fermentation employing B. subtilis and S. griseus can be conducted at temperatures ranging from about 20° C. to about 40° C. For optimum results, it is most convenient to conduct these fermentations at a temperature in the range of from about 24° C. to about 36° C. Temperatures from about 28° to about 34° C. are most preferred. The pH of the nutrient medium suitable for producing the instant compounds can vary from about 6.5 to about 8.0 with a preferred range of from about 6.8 to about 7.3.

The 13-deoxy ivermectin agylcone starting compound is added to the fermentation of the foregoing organisms in quantities of from about 0.1 to about 1.0 g per liter of fermentation medium. It is preferred to use from about 0.1 to about 0.5 g per liter. The 13-deoxy ivermectin aglycone compound may be added at any time during the fermentation cycle. The compound may be added to the medium ingredients before the culture is added and the fermentation begins or they may be added during the course of the fermentation. In order that the cultures have sufficient time to effect the biotransformation, it is preferred that the 13-deoxy ivermectin aglycone starting compound be added to the fermentation before 50% of the cycle is completed, preferably before 25% of the cycle is completed.

Small scale fermentations are conveniently carried out by placing suitable quantities of nutrient medium in a flask employing known sterile techniques, inoculating the flask with either spores or vegetative cellular growth of the foregoing organisms loosely stoppering the flask with cotton and permitting the fermentation to proceed in a constant room temperature of about 30° C. on a rotary shaker at from 95 to 300 rpm for about 2 to 10 days. For larger scale work, it is preferable to conduct the fermentation in suitable tanks provided with an agitator and a means of aerating the fermentation medium. The nutrient medium is made up in the tank and after sterilization is inoculated with a source of vegetative cellular growth of B. subtilis and S. griseus. The fermentation is allowed to continue for from 1 to 8 days while agitating and/or aerating the nutrient medium at a temperature in the range of from about 24° to 37° C. The degree of aeration is dependent upon several factors such as the size of the fermentor, agitation speed, and the like. Generally the larger scale fermentations are agitated at about 95 to 300 rpm and about 50 to 500 liters per minute (LPM) of air.

The separation of the novel compounds from the whole fermentation broth and the recovery of these compounds is carried out by solvent extraction and application of chromatographic fractionations with various chromatographic techniques and solvent systems.

The instant compounds have slight solubility in water, but are soluble in organic solvents. This property conveniently may be employed to recover the compound from the fermentation broth. Thus, in one recovery method, the whole fermentation broth is combined with approximately an equal volume of an organic solvent. While any organic solvent may be employed, it is preferable to use a water immiscible solvent such as ethyl acetate, methylene chloride, chloroform and the like. Generally several extractions are desirable to achieve maximum recovery. The solvent removes the instant compounds as well as other substances lacking the antiparasitic activity of the instant compounds. If the solvent is a water immiscible one, the layers are separated and the organic solvent is evaporated under reduced pressure. The residue is placed onto a chromatography column preferably containing silica gel. The column retains the desired products and some impurities, but lets many of the impurities, particularly the nonpolar impurities, pass through. The column is washed with a moderately polar organic solvent such as methylene chloride or chloroform to further remove impurities, and is then washed with a mixture of methylene chloride or chloroform and an organic solvent of which acetone, methanol, and ethanol and the like are preferred. The solvent is evaporated and the residue further chromatographed using column chromatography, thin layer chromatography, preparative thin layer chromatography, high pressure liquid chromatography and the like, with silica gel, aluminum oxide, ion exchange resins, dextran gels and the like, as the chromatographic medium, with various solvents and combinations of solvents as the eluent. Thin layer, high pressure, liquid and preparative layer chromatography may be employed to detect the presence of, and to isolate the instant compounds. The use of the foregoing techniques as well as others known to those skilled in the art, will afford purified compositions containing the instant compounds. The presence of the desired compounds is determined by analyzing the various chromatographic fractions for biological activity of physico-chemical characteristics. The structures of the instant compounds have been determined by detailed analysis of the various spectral characteristics of the compounds, in particular their nuclear magnetic resonance, mass, ultraviolet and infrared spectra.

The compounds of this invention have significant parasiticidal activity as anthelmintics, insecticides and acaricides, in human and animal health and in agriculture.

The disease or group of diseases described generally as helminthiasis is due to infection of an animal host with parasitic worms known as helminths. Helminthiasis is a prevalent and serious economic problem in domesticated animals such as swine, sheep, horses, cattle, goats, dogs, cats and poultry. Among the helminths, the group of worms described as nematodes causes widespread and often times serious infection in various species of animals. The most common genera of nematodes infecting the animals referred to above are Haemonchus, Trichostrongylus, Ostertagia, Nematodirus, Cooperia, Ascaris, Bunostomum, Oesophagostomum, Chabertia, Trichuris, Stongylus, Trichonema, Dictyocaulus, Capillaria, Heterakis, Toxocara, Ascaridia, Oxyuris, Ancylostoma, Uncinaria, Toxascaris and Parascaris. Certain of these, such as Nematodirus, Cooperia, and Oesophagostomum attack primarily the intestinal tract while others, such as Haemonchus and Ostertagia, are more prevalent in the stomach while others such as Dictyocaulus are found in the lungs. Still other parasites may be located in other tissues and organs of the body such as the heart and blood vessels, subcutaneous and lymphatic tissue and the like. The parasitic infections known as helminthiases lead to anemia, malnutrition, weakness, weight loss, severe damage to the walls of the intestinal tract and other tissues and organs and, if left untreated, may result in death of the infected host. The compounds of this invention have unexpectedly high activity against these parasites, and in addition are also active against Dirofilaria in dogs, Nematospiroides, Syphacia, Aspiculuris in rodents, arthropod ectoparasites of animals and birds such as ticks, mites, lice, fleas, blowfly, in sheep Lucilia sp., biting insects and such migrating dipterous larvae as Hypoderma sp. in cattle, Gastrophilus in horses, and Cuterebra sp. in rodents.

The instant compounds are also useful against parasites which infect humans. The most common genera of parasites of the gastro-intestinal tract of man are Ancylostoma, Necator, Ascaris, Strongyloides, Trichinella, Capillaria, Trichuris, and Enterobius. Other medically important genera of parasites which are found in the blood or other tissues and organs outside the gastrointestinal tract are the filarial worms such as Wuchereria, Brugia, Onchocerca and Loa, Dracunculus and extra intestinal stages of the intestinal worms Strongyloides and Trichinella. The compounds are also of value against arthropods parasitizing man, biting insects and other dipterous pests causing annoyance to man.

The instant compounds are also active against household pests such as the cockroach, Blatella sp., clothes moth, Tineola sp., carpet beetle, Attagenus sp. and the housefly Musca domestica.

The compounds of the present invention are also useful against insect pests of stored grains such as Tribolium sp., Tenebrio sp. and of agricultural plants such as spider mites, (Tetranychus sp.), aphids, Acyrthiosiphon migratory orthopterans such as locusts and immature stages of insects living on plant tissue. The compounds are useful as a nematocide for the control of soil nematodes and plant parasites such as Meloidogyne spp. which may be of importance in agriculture.

The instant compounds can be administered orally in a unit dosage form such as a capsule, bolus or tablet, or as a liquid drench which is normally a solution, suspension or dispersion of the active ingredient usually in water together with a suspending agent such as bentonite and a wetting agent or like excipient. Generally, the drenches also contain an antifoaming agent. Drench formulations generally contain from about 0.001 to about 0.5% by weight of the active compounds. Preferred drench formulations may contain from about 0.01 to about 0.1% by weight. The capsules and boluses comprise the active ingredient admixed with a carrier vehicle such as starch, talc, magnesium stearate, or dicalcium phosphate.

Where it is desired to administer the compounds of the present invention in a dry, solid unit dosage form, capsules, boluses or tablets containing the desired amount of the instant compounds usually are employed. These dosage forms are prepared by intimately and uniformly mixing the active ingredient with suitable finely divided diluents, fillers, disintegrating agents and/or binders such as starch, lactose, talc, magnesium stearate, vegetable gums and the like. Such unit dosage formulations may be varied widely with respect to their total weight and content of the antiparasitic agent depending upon factors such as the type of host animal to be treated, the severity and type of infection and the weight of the host.

When the compounds of the present invention are to be administered via an animal feedstuff, they are intimately dispersed in the feed or used as a top dressing or in the form of pellets which may then be added to the finished feed or optionally fed separately. Alternatively, the antiparasitic compounds of our invention may be administered to animals parenterally, for example, by intraruminal, intramuscular, intratracheal, or subcutaneous injection in which event the active ingredient is dissolved or dispersed in a liquid carrier vehicle. For parenteral administration, the active material is suitably admixed with an acceptable vehicle, preferably of the vegetable oil variety such as peanut oil, cotton seed oil and the like. Other parenteral vehicles such as organic preparation using solketal, glycerol, formal and aqueous parenteral formulations are also used. The compounds of the present invention are dissolved or suspended in the parenteral formulation for administration; such formulations generally contain from about 0.55% to about 5% by weight of the instant compound.

Although the compounds of this invention finds their primary use as an antiparasitic agent in the treatment and/or prevention and treatment of diseases caused by parasites, for example, arthropod parasites such as ticks, lice, fleas, mites and other biting insects in domesticated animals and poultry, they are also effective in treatment of parasitic diseases that occur in other animals including humans. The optimum amount to be employed for best results will, of course, depend upon the species of animal to be treated and the type and severity of parasitic infection or infestation. Generally, good results are obtained with our novel compounds by the oral administration of from about 0.001 to about 10 mg per kg of animal body weight, such total dose being given at one time or in divided doses over a relatively short period of time such as 1-5 days. With the novel compounds of the present invention, excellent control of such parasites is obtained in animals by administering from about 0.025 to about 0.5 mg per kg of body weight in a single dose. Repeat treatments are given where required to combat re-infections and are dependent upon the species of parasite and the husbandry techniques being employed. The techniques for administering these materials to animals are known to those skilled in the veterinary field.

When the compounds described herein are administered as a component of the feed of the animals, or dissolved or suspended in the drinking water, compositions are provided in which the active compound is intimately dispersed in an inert carrier or diluent. By inert carrier is meant one that will not react with the antiparasitic agent and one that may be administered safely to animals. Preferably, a carrier for feed administration is one that is, or may be, an ingredient of the animal ration.

Suitable compositions include feed premixes or supplements in which the instant compounds are present in relatively large amounts and which are suitable for direct feeding to the animal or for addition to the feed either directly or after an intermediate dilution or blending step. Typical carriers or diluents suitable for such compositions include, for example, distillers' dried grains, corn meal, citrus meal, fermentation residues, ground oyster shells, wheat shorts, molasses solubles, corn cob meal, edible bean mill feed, soya grits, crushed limestone and the like. The compounds of the present invention are intimately dispersed throughout the carrier by methods such as grinding, stirring, milling or tumbling. Compositions containing from about 0.005% to about 2.0% by weight of the instant compound are particularly suitable as feed premixes. Feed supplements, which are fed directly to the animal, contain from about 0.0002% to about 0.3% by weight of the instant compounds.

Such supplements are added to the animal feed in an amount to give the finished feed the concentration of active compound desired for the treatment and control of parasitic diseases. Although the desired concentration of the compounds of the present invention will vary depending upon the factors previously mentioned as well as upon the particular compound employed, the compounds of this invention is usually fed at concentrations of between about 0.00001% to about 0.002% in the feed in order to achieve the desired antiparasitic result.

In addition, where the compounds are to be added to an animal's feed it is possible to utilize the dried mycelial cake from the fermentation broth. The mycelia contain a preponderance of the activity and since the level of the activity of the mycelia can be determined, it can be added directly to the animal's feed.

The compounds of this invention also are useful in combatting agricultural pests that inflict damage upon crops while they are growing or while in storage. The compound is applied using known techniques as sprays, dusts, emulsions and the like, to the growing or stored crops to effect protection from such agricultural pests.

The anthelmintic activity of the instant compound may be determined by orally administering via the feed, a sample of the individual compound, a mixture of such compounds, a concentrated extract, and the like to a mouse which had been infected 3 days earlier with a gastrointestinal parasite. At 11, 12 and 13 days after the initiation of the medication, the feces of the mouse are examined for eggs, and on the next day the mouse is sacrificed and the number of worms present in the proximal portion of the small intestine are determined. An active compound is observed when there is a significant reduction of egg and worm counts when compared to infected, unmedicated controls.

The following examples are being provided in order that the instant invention may be more fully understood. Such examples are not to be construed as being limitative of the invention.

The following examples illustrate the present invention without, however, limiting the same thereto.

EXAMPLE 1 A. Fermentation

A frozen vial (2 ml) of Bacillus subtilis MB 4974 (ATCC 55060) was used to inoculate a 250 ml Erlenmeyer flask containing 50 ml of Soy Glucose medium. The seed flask was incubated on a rotary shaker (220 rpm) at 29.5° C. for 24 hours. The developed seed was used to inoculate five 250 ml Erlenmeyer flasks (2.5 ml of seed culture per flask) containing 50 ml each of Soy Glucose Medium. The cells were induced by 18 hour incubation in the presence of 10 μg/ml Immunomycin.

A frozen vial (2 ml) of Streptomyces griseus HCA-185 (ATCC 55070) was used to inoculate a 250 ml baffled Erlenmeyer flask containing 50 ml of Medium A. The seed flask was incubated on a rotary shaker (220 rpm) at 27° C. for 24 hours. The developed seed was used to inoculate five 250 ml Erlenmeyer flasks (5 ml of seed culture per flask) containing 50 ml each of transformation medium B. After 18 hours the cells were induced by exposure to 10 μg/ml of 13-deoxy ivermectin aglycone for 5 hours.

The induced resting cells from 50 ml of medium containing B. subtilis MB4974 cells and from 50 ml of medium containing the S. griseus HCA 185 cells were combined and washed twice with sterile saline, then resuspended in 25 ml of sterile 100 mM MES buffer, pH 6.0 containing 1% glucose. 13-deoxy ivermectin aglycone having the following structure ##STR1## was added to a final concentration of 50 μg/ml, as a DMSO solution. The combined broth was incubated on a rotary shaker (220 rpm) at 27° C. for 18 hours.

B. Isolation and Identification

The whole broth was extracted once with an equal volume of methylene chloride. The methylene chloride layer was evaporated to dryness under reduced pressure, the resulting oil was dissolved in mobile phase and analyzed by HPLC using a Zorbax ODS column. The column was developed with 80% aqueous methanol at 60° C. The 5-β and 13-β ivermectin monoglucopyranosides, as well as 13-β ivermectin aglycone and unconverted 13-deoxy ivermectin aglycone were identified by retention time, compared to authentic standards.

After 24 hours incubation, HPLC incubation, HPLC analysis determined that less than 5 μg/ml of 13-deoxy ivermectin aglycone remained. The major product was 13-β ivermectin monoglucopyranoside I, with smaller amounts of 5-β ivermectin monoglucopyranoside II and 13-β ivermectin aglycone. ##STR2## 

What is claimed is:
 1. A fermentation medium containing B. subtilis and S. griseus and a fermentation substrate that is 13-deoxy ivermectin aglycone.
 2. A fermentation medium according to claim 1 wherein the B. subtilis is strain ATCC
 55060. 3. A fermentation medium according to claim 1 wherein the S. griseus is strain ATCC
 55070. 4. A fermentation medium according to claim 1 wherein the B. subtilis is strain ATCC 55060 and the S. griseus is strain ATCC
 55070. 5. A fermentation medium according to claim 1 that contains a recoverable amount of 13-β ivermectin monoglucopyranoside.
 6. A fermentation medium according to claim 1 that contains a recoverable amount of 5-β ivermectin monoglucopyranoside.
 7. A fermentation medium according to claim 1 that contains a recoverable amount of 13-β ivermectin monoglucopyranoside and of 5-β ivermectin monoglucopyranoside. 